Vehicles may include a coolant system configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, a coolant is circulated through the engine (e.g., through an engine block), where heat is transferred from the hot engine to the coolant, and then circulated through a radiator near the front of the vehicle, where heat is transferred from the coolant to the ambient air. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The coolant system may include various components, such as various valves, pumps, and one or more thermostats.
Various approaches have been developed to address engine overheating in the event of coolant system degradation. One example approach is shown by Willard et al. in U.S. Pat. No. 9,217,379. Therein, a method is disclosed for addressing engine overheating by alternately shutting down fuel to one or more cylinders while maintaining vehicle torque demand with the fueled cylinders. In still other examples, the engine may be cooled bank-wise, with fuel shut off to each cylinder of a first bank to cool the first bank while fuel is delivered to each cylinder of a second bank to continue to generate torque for vehicle propulsion.
However, the inventor herein has recognized potential issues with such systems. As one example, while heat may be transferred from the hot engine to the cool air flowing through the unfueled cylinders, air is a poor heat conductor. Additionally, high under-hood temperatures may be exacerbated on a hot day, which may raise the temperature of the air being pumped through the engine.
Further, the inventor herein has recognized that a combination of variable displacement engine (VDE) technology and direct injection technology may be utilized to cool the engine. Variable displacement engines are configured to operate with a variable number of active or deactivated cylinders to increase fuel economy. For example, a portion of the cylinders may be deactivated during selected conditions, such as during low engine torque demand. A control system may selectively deactivate cylinders via a plurality of cylinder valve deactivators, thereby sealing the deactivated cylinders by maintaining intake and exhaust valves of the deactivated cylinders closed. Typically, the deactivated cylinders are not fueled. However, the inventor herein has recognized that liquid fuel has a higher thermal conductivity than air, which may increase a rate of engine cooling compared with air. Additionally, a change in state of the liquid fuel as it vaporizes within the deactivated cylinders may further improve engine cooling.
In one example, the issues described above may be addressed by a method, comprising: deactivating a subset of cylinders of a multiple cylinder engine based on a temperature of the engine; and directly injecting fuel into each of the subset of cylinders during the deactivation. In this way, an overheated engine may be cooled with liquid fuel, increasing a rate of cooling compared to when the engine is cooled with air.
As one example, deactivating the subset of engine cylinders includes maintaining intake and exhaust valves coupled to each of the subset of engine cylinders closed. In this way, each of the subset of engine cylinders is sealed. By directly injecting fuel into the sealed cylinders, the fuel will remain in the sealed cylinders until the corresponding intake and exhaust valves are reactivated and opened. Furthermore, a spark plug coupled to each of the subset of engine cylinders may be disabled so that spark is not provided and combustion does not occur in each of the subset of engine cylinders. The liquid fuel may be injected into the sealed cylinders at a plurality of piston positions in order to coat various cylinder surfaces (e.g., top, bottom, and walls) and agitated within the sealed cylinders by the piston, absorbing heat from the hot cylinder surfaces. After the liquid fuel is vaporized (e.g., after a duration of agitation), the intake and exhaust valves of each of the subset of engine cylinders may be opened in order to exhaust the vaporized, uncombusted fuel. The process of deactivating the subset of engine cylinders and directly injecting fuel into each of the subset of engine cylinders during the deactivation may be repeated until the engine is sufficiently cooled (e.g., the engine temperature is less than a threshold temperature). Further still, cooling the engine with liquid fuel may be combined with air cooling methods, with the cooling method selected based on operating conditions, for greater flexibility. By utilizing VDE technology to deactivate and seal the subset of engine cylinders and injecting liquid fuel directly therein, the engine may be cooled at a faster rate than if airflow through the engine is used, preventing engine overheating-related degradation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.